PROJECT 2: Summary/Abstract Despite a variety of screening approaches, an estimated 135,000 persons will be diagnosed with colorectal cancer (CRC) in 2017, and about 50,000 will die from it. Evidence is increasing that signal transducer and activator of transcription (STAT) 3 contributes to patients at increased risk for CRC, such as those with inflammatory bowel disease (IBD) and patients with hereditary syndromes, such as familial adenomatous polyposis (FAP) and Lynch syndrome (LS). The importance of STAT3's contribution to CRC in these settings and the effects of targeting STAT3 on CRC development and disease progression are the significant gaps in knowledge for this project. We and others have demonstrated that colitis in mice induced by either dextran sodium salt [DSS; ulcerative colitis (UC) model] or trinitrobenzoic acid [TNBS; Crohn's disease (CD) model] is more severe and progresses more rapidly to CRC in transgenic mice expressing only STAT3?, the pro- inflammatory and anti-apoptotic isoform of STAT3, compared to wild type mice. In collaboration with our pharmaceutical partner (StemMed, Ltd.), we developed a small-molecule, C188-9, that potently inhibits STAT3 activation [phosphorylation on tyrosine (Y) 707, pY-STAT3], which prevented IBD caused by both DSS and TNBS in mice. Others have shown that mice deficient in Stat3 in their intestinal epithelial cells have reduced tumor size and reduced tumor incidence in a model of colitis-associated CRC [azoxymethane (AOM) plus DSS]. Also, genetically reducing levels of STAT3 in the ApcMin/+ mouse (ApcMin/+Stat3+/?) reduced the number of intestinal polyps compared to ApcMin/+Stat3+/+ mice while STAT3 activation resulted in extra-nuclear sequestration of hMSH3, which may further impair dMMR in enterocytes from LS patients thereby resulting in increased risk of CRC. The long-term goal of this project is to determine if C188-9 will be of benefit in the prevention and/or treatment of CRC. The central hypotheses are that STAT3 contributes to CRC development in patients at risk for CRC and can be targeted successfully with C188-9. The objectives are to determine the effects of targeting STAT3 using C188-9 to prevent CRC in mouse models of IBD, FAP, and LS and to determine the contribution of STAT3 signaling to CRC development in corresponding patient subsets. We have formulated 3 tightly focused Specific Aims to examine these hypotheses and to achieve these objectives. In Aim 1, we will determine the ability of C188-9 to prevent CRC in mouse models of IBD and hereditary CRC. In Aim 2, we will audit the contribution of STAT3 signaling to CRC development in FAP, LS and IBD patients, including in viable patient- derived colonic organoids. Lastly, in Aim 3, we will determine the effect on pY-STAT3 and safety of chronic exposure to C188-9 as chemopreventive agent in high-risk colorectal cancer patients diagnosed with IBD, LS and FAP treated in the context of a Phase Ib chemopreventive clinical trial. The results of these studies will provide critical information regarding the contribution of STAT3 to CRC development and support further clinical studies examining C188-9 in the prevention of CRC.